Nylon fiber blends



United States Patent 3,188,790 NYLON FIBER BLENDS Harold H. Hebeler, Seaford, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware No Drawing. Filed June 12, 1963, Ser. No. 287,195

9 Claims. (Cl. 57-140) This invention relates to new textile products, and is more particularly concerned with a blend of synthetic staple fibers and with its use for blending with and reinforcing natural fibers. This application is a continuationin-part of my copending application Serial No. 152,314, filed November 14, 1961, as a division of my application Serial No. 668,718, which was filed June 28, 1957, and issued a US. Patent No. 3,044,250 on July 17, 1962.

The preparation of uncrimped staple fiber. of synthetic linear condensation polymer, suitable for blending with natural fibers such as' cotton to impart both improved abrasion resistance and increased tensile strength. is fully described in my US. Patent No. 3.044.250. This patent .simultaneously being heated, the product of the tempera- -ture of heating in degrees centigrade and the time of heating in seconds being at least about 200 and preferably from about 1000 to 6000. The resulting fibers are characterized by being highly oriented and highly crystalline. The fibers are not crimped because the heat required in conventional crimping processes would produce an amount of relaxation in these nylon fiber which results in too much less of load-bearing capacity at low elongations.

In the preparation of yarns from blends of different types of fibcrs, one has a choice of several points in the 1 process at which the different fibers may be brought together. For example. the fibers may be mixed before 7 they are supplied to the picker hopper. they may be proc- "essed separately through breaker lap and the blend made on the finisher picker, or the different fibers may be processed separately into sliver and combined on the draw frame. The most economical operation, with the formation of the least amount of mixed waste fiber, involves blending at the draw frame. However. when using highly oriented and crystalline nylon staple fibers, blending at the draw frame has required that uncrimped staple fiber be processed through the picking and carding operations. Unfortunately, it has been found that the carding of this uncrimped nylon staple is accompanied by excessive loading of the main cylinder of the card, especially when metallic clothing is used, and by poor web and lap cohesion. with the result that this potentially economical method of preparing a blended nylon and cotton yarn has not been practicable.

The present invention provides a method of overcoming this problem in preparing nylon/cotton blends. The invention is also applicable to preparing blends of other fibers, such as polyethylene terephthalate staple fiber and cotton. However, since crimped fibers of polyethylene terephthalate can readily be prepared to have load-bearing capacities higher than cotton at low clongations, there will normally be no reason to use any uncrimped polyester staple fibers. Therefore. the disclosure will be concerned primarily with the special problem of preparing nylon blends.

It is an object of this invention to provide a nylon 3,188,790 Patented June 15, 1965 staple fiber product of improved cardability, suitable for forming nylon/cotton blend yarns of high strength and abrasion resistance. Another object is the use of the product to provide improved processability on cotton system equipment for reinforcing natural fibers. A further object is to make possible more economical pro- 'duction of high strength blended staple yarns. Further objects will appear as the description of the invention proceeds.

It has now been discovered that the picking and carding of uncrimped nylon staple fibers is greatly facilitated by the addition of relatively small quantities of crimped nylon staple fibers. Therefore, the objects of this invention are obtained by a combination of crimped and uncrimped nylon staple fiber comprising 50 to of an uncrimped nylon staple fiber characterized by having both a high degree of crystallinity and a high degree of crystalline orientation such that it has a time-stable load-bearing capacity at least equal to that of cotton fibers at the break elongation characteristic of cotton fibers, and 50-10% ofa crimped nylon staple having a crimp index of at least 8%.

Surprisingly, the nylon staple of this invention achieves improved processability in the picking and carding operations while at the same time affording superior reinforcing properties for natural fibers, such as cotton, in blended staple yarns.

The term nylon as used herein refers to high molecu lar weight fiber-forming polycarbonamides, e.g., polyhexamethylene adipamide (66 nylon) and polycaproamide (6 nylon).

The uncrimped high load-bearing nylon fiber component of the staple of this invention is that described in my US. Patent No. 3,044,250, and may be prepared by methods described therein. The fiber is characterized by a density higher than about 1.139 gm./cc. and a birefringence above about 0.0590. The fiber is further characterized by a load-bearing capacity at an elongation of 7% (hereinafter designated T greater than 2.1 grams per denier, measured after 9 days slack aging. The nylon staple is further characterized by a boil-off shrinkage (shrinkage determined by boiling a previously measured skein in water for 60 minutes) of less than about 6%. The term uncrimped fiber," as used herein,'means a fiber having a crimp index of substantially zero.

Crimp index is determined on individual filaments by (a) straightening a fiber to remove crimp without substantial elongation of the fiber, (b) measuring the straightcned length, (c) allowing the fiber to retract freely and iigflill measuring; the crimp index i calculated as folows:

Length (a) -longl h( c) Length (a) The crimped nylon fiber component of the staple of X crimp index this invention is characterized chiefly by its crimp index,;' which is preferably'in the range from 15% to 30%.

Fiber which has a crimp index less than about 8% does not give the improved ;r'ii'ocessability characteristic of the staple of this invention? While fiber having a crimp index greater than 30% can be used to provide improved processability, it is not as desirable for this purpose, al-- among which may be mentioned the regular crimp produced by gear crimping and the helical crimp produced by twisting and heat setting. The production of helical crimp with false twisting apparatus 'is disclosed in 'Breen et al. U.S. Patent No. 3,079,745 and in the patents referenced therein. This type of crimp is illustrated in Billion U.S. Patent No. 2,957,224. Edge crimpers of the type disclosed in Pittman et a]. U.S. Patent No. 3,047,932 provides suitable crimp Non mechanical crimp is suitable, such as the random, three-dimensional nonhelical curvilinear configuration produced with a jet of heated fluid, e.g., as disclosed in Hallden et al. U.S. Patent. No. 3,005,251. v

The jcrimped nylon component, which may be referred to as the carrier fiber, of the staple of this invention may be prepared from the same polymer as the uncrimped component, or from a different nylon polymer. Likewise, the crimped fiber may have the same or different denier per filament, the same or different cut length, and the.

same or different filament cross-section. As pointed out previously, the essential feature is that the uncrimped, high load-bearing staple fiber be mixed with to 50% of a nylon fiber having a crimp index of at least 8% and prefcrably in the range of from to In a preferred embodiment, where it is desired that the two components of the nylon staple of this invention have the same dyeing properties, the 'crimped portion is prepared in substantially the same manner as the high 'T uncrimped portion, but with the additional step of crimping being added after the drawing heat-treating step, which may be accomplished either as a separate step or integrated in the drawing heat-treating step. The similar preparation of both components avoids dissimilarities of internal structural features in respects which would cause differences in dye receptivity. The dying rates of the two components are nearly equivalent, with a consequent improvment in dyeing uniformity in the finished textile article.

For best results in processing on cotton system equipment, it ispreferred that the crimped and uncrimped components of the staple of this invention have substantially the same cut length.

The staple of this invention is readily prepared by combining tows of crimped and uncrimped continuous fibers in the desired proportions and feeding the combined tow to a conventional staple cutter. The product issuing from the cutter is an intimate uniform blend of crimped' and uncrimped staple fibers.

In another embodiment, a continuous filament is first crimped and then cut into staple. This crimpccl fiber is blended with separately cut, uncrimped fiber to serve as the carrier fiber for the uncrimped component.

The birefringence of the yarn is determined according to methods of Heyn, Textile Research Journal 22, No.

513 (1952), and is a measure of structural orientation. The density is measured using density gradient tubes, according to the method of Boyer, Spencer and Wiley, Journal of Polymer Science 1, N0. 249 (1946). The density is proportional to the degree of crystallinity of the fiber.

The invention is further illustrated by the following examples which are intended to be illustrative and not limitative. w v

EXAMPLE I 7 Polyhexamethylene adipamide is melt spun and drawn according to the method described in my U.S. Patent 3,044,250 to give a 2.3 denier per filament (0.256 tex. per filament) uncrimped tow in which the filaments have the following properties: a density of 1.14 grams per cc., a birefringence of 0.0594, a tenacity of 6.6 grams per denier, a break elongation of 22%, a boil-off shrinkage of 5.1%, and a load-bearing capacity at 7% elongation (T of 2.3 g.p.d. The crimp index of these filaments is .substantially zero. This tow is referred to as the high T component. 1

Polyhexamethylene adipamide is also used to prepare two low modulus, commercial grade, crimped tows, A and B, by conventional methods to serve as carrier fibers for the above high T tow. The crimp is that provided by a conventional stutfer box crimper as disclosed in Hitt U.S. Patent No. 2,311,174. Tow A is composed of filaments having a denier of 1.5 (0.167 tex.), a tenacity of 4.0 g.p.d., a break elongation of 36%, a T value of 0.9 g.p.d., and an average crimp index of 18% Tow B is composed of filaments having a denier of 3.0 (0.333 tex.), a tenacity of 4.1 g.p.d., a break elongation of 36%, a T

I value of 0.9 g.p.d., and an average crimp index of 20%.

The uncrimped high T tow is combined with each of tows A and B in weight ratios 20/80, /65, and 50/50 (crimped/uncrimped), and cut to staple having a length 1.5 inches. These six staple blends are then picked and carded on cotton system equipment, along with a control item composed of the high T fibers only. The high T control gives excessive card loading as well as poor web cohesion. In contrast, each of the other six staple items exhibits markedly reduced card loading and gives significantly higher web cohesion. Y

Each of theabove seven nylon staple items is used to prepare a nylon/cotton yarn of 50/50 composition by blending the nylon sliver with a middlings cotton sliver ona draw frame. Each of these nylon/cotton blends is split during spinning to produce two yarns, a filling yarn of 17.5/1s cotton count construction, 3.3 twist multiplier, and a warp yarn of 21/1s cotton count, 4.75 twist multiplier. The strength of each product is determined and reported as Lea product (skein break factor) in the table below. 7 v

The data in Table I shows that, althoughsubstitution of crirnped nylon carrier fiber for part of the high T component in the cotton/nylon blend yarn reduces the yarn strength somewhat, the yarn is still stronger than a cotton yarn. This result is in contrast to that obtained with a nylon-cotton blend yarn containing less than 50% nylon in which there is no high T component. yarns are always weaker than 100% cotton yarn.

Similar results are obtained when the uncrimped high Such T component is composed of filaments having a ,denier of 1.5 (0.167 tex.). Substantially equivalent. results are ob-- tained when the nylon fibers of the example are prepared from polycaproamide.

Table l Spun Yarn Blend Composition Len Product- Carrier Qarrler High T Cotton, Fiber A, Fiber B, percent percent 17.5/ls cc. 21/1's cc.

percent percent so so 2. 634 2, 441 10 r 40 50 2. 366 2, 17. d 32. 5 50 2, 289 2, 054 25 25 50 2. 019 1, 911 40 50 2, 332 2, 085 32. 5 50 2, 260 2, orrz 25 50 1, 980 1, 850 100 1, B25 1, 725

EXAMPLE II and thereby indicate the effect'on web strength.

Selected blends of the high T staple and carrier fibers A and B prepared in Example I are processed through the picker and card to produce card slivers which are tested for strength on a Uster Tester as follows: Card sliver is passed through two sets of two rolls each and between which a speed differential exists such that a small amount (1.78X) 'of drafting takes place. The downstream roll set is on a flexible mount, and moves back and forth as the sliver cohesion varies. an electric signal to a recorder througha transducer cir- This movement sends.

cuit. The recorder is calibrated to read the sliver pull force (i.e., the flexible mount movement) in milligrams. The strength of each sliver is reported in Table II in terms of milligrams per denier.

The data in the table clearly shows that the blends containing a carrier fiber produce card slivers having a significantly higher strength than the control samples.

EXAMPLE llI Polyhexamethylene adipamide is melt spun and drawn, according to the method described in my U.S. Patent No. 3,044,250, to become an uncrimped tow identical to the high T7 sample of Example I.

Polyhexamethylene adipamide is also used to prepare a high modulus crimped tow to serve as carrier fibers for the high T tow of this Example III. This crimped tow may be prepared either by crimping high T, tow in the integrated process of drawing and crimping, or by a separate step. In either case, a stuffer box crimper is used, as disclosed in Hitt US. Patent No. 2,311,174, and sufficient plasticity of the tow may be achieved through moisture addition to facilitate crimp formation. This crimped tow is composed of filaments having a denier of 3.0. a tenacity of 4.1 g.p.d., a break elongation of 36%, a T value of 0.9 g.p.d., and an average crimp index of 8%.

A staple blend of the uncrimped high T7 tow for this l-Txample Ill (84%), with the high modulus crimped tow of this Example 111 (16%). is picked and carded on cotton system equipment and a significantly high web colicsion as well as a reduced card loading is experienced.

A nylon/cotton yarn of l8/82 composition is prepared by blending the nylon blend sliver of this Example 111 with a middlings cotton sliver on a draw frame. This nylon/cotton blend is split during spinning to produce two yarns, a filling yarn of 17.5/ls cotton count construction, 3.3 twist multiplier. and a warp yarn of 21/1s cotton count, 4.75 twist multiplier. The Lea products of the warp yarn and of the filling yarn show that each yarn is much stronger than an equivalent 100% cotton yarn. Web strength for the nylon staple blend of this Example 111 is significantly higher than the strength of an all-high T control.

The Warp yarn and the filling yarn of this example are woven into denim and other heavy service fabrics which unexpectedly exhibit superior serviceability.

The improvement afforded by the nylon staple blends of this invention is obtained over a wide range of filament deniers, e.g., from 1.2 to denier and above. Likewise, the invention is not limited to any particular length. Any staple length suitable for blending with cotton may be used, e.g.. 1", 1%", 1 /2", 1%", 2", 2 /2", 3", 4", and others. Where the nylon blendis to be used for reinforcing fibers other than cotton (such as viscose rayon, acetate rayon, and other cellulosic derivatives, as well as protein fibers and such synthetic fibers as polyacrylonitriles and polyolefins) other staple cut lengths may be used as suitable for each fiber to be reinforced.

Although the invention has been illustrated in the examples primarily with nylon staple fibers' prepared from polyhexamethylene vadipamide, other synthetic linear condensation polymer fibers, including both nylon and polyester fibers, may be used. The invention may be applied generally to fibers of any synthetic linear polymer having recurring units of the formula -l t t as integral parts of the main polymer chain, wherein R is hydrogen or a monovalent hydrocarbon radical, the average number of carbon atoms separating the amide groups being at least two, said polycarbonamide having an intrinsic viscosity of at least about 0.4, as defined in Carothers US. Patent No. 2,130,948, dated September 20, 1938. Particular polycarbonamides included among those which are useful in this invention are as follows: polyhexamethylene adipamide, polyhexamethylene seb'acamide, polymerized o-aminocaproic acid, polytetramethylene sebacamide, polytetramethylene adipamide, polymetaxylylene adipamide. the polyamide from bist4-aminocyclohexyl)methane and azclaic acid, sehacic acid or decamethylene-l,lO-dicarboxylic acid, and the polyamide from 2-methylhexamethylene diamine and terephthalic acid. The invention is also applicable to various copolymers, either block or random, such as the copolymer of polyhexamethylene adipamide and polyhexamethylene isophthalamide, and the copolymer of polyhexamethylene adipamide and polyhexamethylene-t-butyl isophathalamide.

The nylon staples of this invention may contain conventional delustrants, dye modifiers, antistatic agents, antioxidants, heat stabilizers and the like. Suitable staple finishes may be added to the fibers as desired.

The present invention offers a distinct improvement over the prior art. It provides for improved and more economical processing of nylon staples especially suitable for reinforcing natural fibers such as cotton. The blended yarn produced may be fashioned into wearing apparel, industrial fabrics, sheeting, and like articles which are characterized by improved wear and abrasion resistance.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

I claim:

1. A combination of crimped and uncrimped nylon staple fiber suitable for blending with cotton fiber, comprising a mixture of 50% to of uncrimped nylon staple fiber characterized by a load-bearing capacity of at least 2.1 grams per denier at 7% elongation and a boil-off shrinkage of not over 6%, both properties measured after 9 days slack ageing, and 50% to 10% of crimped nylon staple fibers having a crimp index of at least 8%.

2. A product as defined in claim 1 wherein the nylon fibers are of polyhexamethylene adipamide.

3. A product as defined in claim 2 wherein the uncrimped fibers are further characterized by a birefringence of at least 0.0590 and an average density above about 1.139 grams per cubic centimeter.

4. A product as defined in claim 1 wherein the crimped stable fiber has a crimp index of 15% to 30%.

5. A product as defined in claim 1 wherein the crimped staple fiber component is obtained by crimping said uncrimped staple fiber.

6. A yarn composed of a blend of cotton and a mixture of 50% to 90% of uncrimped nylon staple fiber characterized by a load-bearing capacity of at least 2.1 grams per denier at 7% elongation and a boil-off shrinkage. of not over 6%, both properties measured after 9 days slack ageing, and 50% to 10% of crimped nylon staple fiber having a crimp index of at least 8%.

7. A yarn as defined in claim 6 whereinthe nylon References Cited by the Examiner fibers are of polyhexamethylene adipamide.

8. A yarn as defined in claim 6 wherein the crimped UNITED STATES PATENTS staple fiber has a crimp index of 15% to 30%, 7 1,172,439 9/39 Dr ey fus et a1 57 14 9. A yarn-as defined in claim 6 ,eomposed of about 5 2,636,222 4/53 Wllkle r 50% to 82% of cotton, the remainder being the mixture 2,851,737 9/58 Hume! 31 of crimped and uncrimped nylon staple fiber, th yarn 7 11/61 Moler 57 14 having a Lea products strength greater than that Of an equivalent 100% cotton yam. MERVIN STEIN, Primary Examiner. 

6. A YARN COMPOSED OF A BLEND OF COTTON AND A MIXTURE OF 50% TO 90% OF UNCRIMPED NYLON STAPLE FIBER CHARACTERIZED BY A LOAD-BEARING CAPACITY OF AT LEASR 2.1 GRAMS PER DENIER AT 7% ELONGATION AND A BOIL-OFF SHRINKAGE OF NOT OVER 6%, BOTH PHOPERTIES MEASURED AFTER 9 DAYS SLACK AGEING, AND 50% TO 10% OF CRIMPED NYLON STAPLE FIBER HAVING A CRIMP INDEX OF AT LEAST 8%. 